1. Field of the Invention
The present invention generally relates to a combination gear, and more particularly, to a combination gear having a gear slipping-off preventing structure with an easier combining operation.
2. Description of the Related Art
A duplex gear (or two-stage gear) having a small gear portion and a large gear portion with a common shaft and integrally formed with the same material is known as a reduction gear to be used in a power transmission mechanism.
The small gear portion, however, of course has a smaller pitch circle diameter than that of the large gear portion. Accordingly, force to act on the small gear portion is large, and wear of the gear teeth of the small gear portion arises, especially in case material of the small gear portion is softer than that of the large gear portion.
FIG. 3 shows, for example, a part of a moving mechanism of a replaying portion of a disk in a disk changer. In this mechanism, transmission of power is carried out from a spur gear 2 made of resin to a large gear portion of a duplex gear 1. Next, power is transmitted from a small gear portion of the duplex gear 1 to a sector gear 3 made of metal. In this mechanism, a resin should be preferably used as a material of the duplex gear 1 from viewpoint of its cost. Form viewpoint of durability of the small gear portion to engage the sector gear 3 made of metal, however, the duplex gear 1 is made of metal. That is, the duplex gear 1 made of metal causes to increase weight of the gear mechanism, besides to increase the cost.
As is shown in FIG. 4, in order to improve the above, a duplex gear, namely a combination gear 4, consisting, separately, of a large gear 4a made of resin and a small gear 4b made of metal has been used, thereby attaining cost reduction and light-weighing.
This combination gear 4 has a coupling female-portion 4c of the large gear 4a and a coupling male-portion 4d of the small gear 4b as coupling portions. The combination gear 4 is formed by putting them together in an axial direction.
With respect to the combination gear 4, however, when the combination gear 4 is driven after the shaft 6 has been inserted therein, force to separate the combined small and large gears 4a,4b and arises its axial direction caused by backrush of the coupling male- and female-portions, which requires to provide a slipping-off preventing member 5 to hold the coupling of the combination gear 4 on the shaft 6, thereby preventing downsizing or thin-modeling of the gear mechanism.
In view of the foregoing, an object of the present invention is to provide a combination gear having a gear slipping-off preventing structure with an easier combining operation.
In order to achieve the above-described object, as a first aspect of the present invention, a combination. gear having a gear slipping-off preventing structure includes: a first gear having a shaft hole; a second gear, having a shaft hole, to coaxially couple with the first gear so as to constitute the combination gear; and a shaft to be inserted into the shaft holes of the respective first and second gears, wherein either one of the first and second gears is provided with a coupling male-portion having a securing projection and the other of the first and second gears is provided with a coupling female-portion having a securing recess so that the first and second gears combine together by coupling the coupling male-portion with the coupling female-portion with an engagement between the securing projection and the securing recess.
As a second aspect of the present invention, in the structure with the above first aspect, a relief portion to permit a relief of an end portion of the securing projection on coupling the coupling male-portion with the coupling female-portion is provided inside the securing recess.
As a third aspect of the present invention, a combination gear having a gear slipping-off preventing structure includes: a first gear having a shaft hole; a second gear, having a shaft hole, to coaxially couple with the first gear so as to is constitute the combination gear; and a shaft to be inserted into the shaft holes of the respective first and second gears, wherein either one of the first and second gears is provided with a coupling male-portion having a securing recess and the other of the first and second gears is provided with a coupling female-portion having a securing projection so that the first and second gears combine together by coupling the coupling male-portion with the coupling female-portion with an engagement between the securing projection and the securing recess.
As a fourth aspect of the present invention, in the structure with the above third aspect, a relief portion to permit a relief of an end portion of the securing projection on coupling the coupling male-portion with the coupling female-portion is provided inside the securing recess.
According to the above-described structure of the present invention, because the gears of the combination gear are engaged with each other in the axial direction, even if force, caused by the backrush between the coupling male- and female-portions, to separate the both gears arises in the axial direction, the coupling of the combination gear does not be released as long as the shaft is inserted therein. And, the combination gear of the present invention does not require any slipping-off preventing member on the shaft, thereby attaining reduction of parts and downsizing and thin-modeling of the combination gear itself.
And, because the relief recess is provided at the engaging portion, efficiency of the coupling work of the combination gear can be improved.